Bradycardia-dependent block in the accessory pathway in a patient with alternans Wolff-Parkinson-White syndrome

Abstract

Although the intermittent preexcitation in the WolffParkinson-White (WPW) syndrome is a well-known phenomenon manifested by abrupt loss of delta wave from 1 beat to the next on the electrocardiogram (ECG), the occurrence of WPW syndrome on alternate beats during regular cardiac rhythm has been observed occasionally on rhythm strips. -5 We report a case of probable bradycardiadependent block in the accessory pathway in a patient with alternans WPW syndrome during regular sinus rhythm. A 57-year-old woman presented to the hospital with a 12-lead ECG recorded during a routine examination for arterial hypertension. She denied history of episodes of tachycardia and was receiving captopril. The patient’s initial physical examination, biochemical profile, and chest x-ray were all normal. The admission ECG (Fig. 1) showed regular sinus rhythm at 95 beats/min and 2 different types of QRS complexes on alternate beats: (a) a narrow QRS complex (0.08 second) showing PR interval of 0.16 seconds and a negative T wave in the inferior leads (arrows), and (b) a wide QRS complex (0.12 seconds) revealing short PR interval of 0.10 to 0.11 seconds and WPW conduction with upright delta wave in lead V2 to V6, I, and aVL (type B). There was also RR interval alternans. The shorter RR interval of 580 milliseconds was followed by a broad QRS complex with WPW pattern, and the longer RR interval of 680 milliseconds was followed by a normal conduction. In the precordial leads, alternans WPW syndrome was followed by a premature ventricular contraction (asterisk). The subsequent long compensatory pause of 880 milliseconds terminated with a narrow QRS complex (suggesting bradycardia-dependent block in the bypass tract), which begun another episode of alternans WPW syndrome. The next ECG obtained several minutes later revealed normal ventricular conduction, with disappearance of the wide QRS complex characteristics of WPW syndrome. Alternans WPW could not be induced either spontaneously or/nor